Translational and rotational diffusion of a small globular protein under crowded conditions - PubMed (original) (raw)

Translational and rotational diffusion of a small globular protein under crowded conditions

Conggang Li et al. J Phys Chem B. 2009.

Erratum in

Abstract

Protein-protein interaction is the fundamental step of biological signal transduction. Interacting proteins find each other by diffusion. To gain insight into diffusion under the crowded conditions found in cells, we used nuclear magnetic resonance spectroscopy (NMR) to measure the effects of solvent additives on the translational and rotational diffusion of the 7.4 kDa globular protein, chymotrypsin inhibitor 2. The additives were glycerol and the macromolecular crowding agent, polyvinyl pyrrolidone (PVP). Both translational diffusion and rotational diffusion decrease with increasing solution viscosity. For glycerol, the decrease obeys the Stokes-Einstein and Stokes-Einstein Debye laws. Three types of deviation are observed for PVP: the decrease in diffusion with increased viscosity is less than predicted, this negative deviation is greater for rotational diffusion, and the negative deviation increases with increasing PVP molecular weight. We discuss our results in terms of other studies on the effects of macromolecules on globular protein diffusion.

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Figures

Figure 1

Figure 1

15N filtered 1H spectra of 1mM 15N enriched chymotrypsin inhibitor 2 in 100 g/L 10 kDa PVP (50 mM acetate buffer; pH 5.4; 25°C; 0.3 s diffusion time; 0.02 ms gradient duration) with increasing gradient strength (G/cm).

Figure 2

Figure 2

Translational diffusion results for chymotrypsin inhibitor 2 in 1:1 (g/g) mixture of 40 kDa :10 kDa PVP [Red, 100 g/L; green, 200 g/L; blue, 300 g/L, b = (γGδ)2Δ]. The conditions are defined in the caption to Figure 1.

Figure 3

Figure 3

Translational (A) and rotational (B) diffusion of chymotrypsin inhibitor 2 in a small molecule, glycerol (—) and family of differently sized polymers [10 kDa PVP (••), 40 kDa PVP (– –), 1:1 (g/g) mixture of 40 kDa :10 kDa PVP (– ••)]. The conditions are defined in the caption to Figure 1. The colors are defined in the caption to Figure 2. The curves for PVP are of no theoretical significance. For glycerol, the line extends beyond the points to illustrate the Stokes Einstein and Stokes Einstein Debye relationships. The data for 40 kDa PVP have been published.

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